1. Field of the Invention
The present invention relates to packages for semiconductor chips or other electronic devices.
2. Background Information
A typical package for a semiconductor chip includes an internal metal leadframe, which functions as a substrate for the package. The leadframe includes a central die pad and a plurality of leads that radiate outward from the die pad. A hardened, insulation encapsulant material covers the chip, die pad, and an inner portion of each of the leads.
The semiconductor chip is mounted on the die pad and is electrically connected to the leads. In particular, the chip includes a plurality of bond pads, each of which is electrically connected by a bond wire or the like to a bond finger that is at an inner end of one of the leads. An outer portion of each lead extends outward from the encapsulant, and serves as an input/output terminal for the package. The outer portion of the leads may be bent into various configurations, such as a J lead configuration or a gull wing configuration.
In the market for semiconductor packaging today, there is a trend toward decreasing the size of leadframes and packages. This is driven by semiconductor chip size reductions that accompany each new generation of fabrication processes. As the chip size shrinks, so must either the bond finger pitch, or the number of bond fingers located proximate to the die pad, otherwise wire lengths get too long and mold yield suffers due to wire sweep.
Reducing the number of bond fingers located proximate to the die pad can be difficult. This is especially true given that, as the size of a semiconductor chip decreases, the number of electrical connections it requires does not. Accordingly, an improved method of making a leadframe is desirable.
An exemplary embodiment of the present invention is a leadframe that provides both short leads and long leads. The short leads are situated within unused space that is created between the long leads as the long leads fan out towards the outer edges of the leadframe. The inner end segments of the longer leads are adapted to accommodate two or more electrical connections, and these added electrical connections are then routed back to the short leads. The resulting leadframe requires less inner end segments proximate to the die pad and allows for the creation of smaller leadframes. Correspondingly smaller packages can be made with such leadframes than is achievable with leadframes made only by conventional methods.
In accordance with one embodiment of the invention, a leadframe comprises a plurality of metal leads extending from a metal frame, each lead including an inner end segment beginning at an inner end of the lead, a nonconductive layer on the inner end segment of at least one of the leads and set back from its inner end, and an electrically conductive layer on a surface of the nonconductive layer and generally parallel to a longitudinal direction of the inner end segment, wherein the nonconductive layer electrically isolates the electrically conductive layer from the respective lead upon which the nonconductive layer is positioned. In some embodiments, the inner end segment of each of a first subset of the leads extends further toward a center of the lead frame than the inner end segment of each of a second subset of the leads.